Three-axis stabilized satellites, especially geosynchronous satellites, comprise often a three-axis gyro package with the help of which attitude changes of the satellite, meaning rotations around one or several of the three axes of the coordinate system fixed with respect to the satellite, can be monitored by measurements. The premise for a trouble-free measurement is herein the principle that the gyros, whose axes of rotation are arranged parallel to the respective axes of the coordinate system fixed with respect to the satellite, reflect their rotations explicitly by their output signals. It has however been seen that the gyros tend to drift, meaning they supply an output signal even when no rotations have occurred. The extent of these drifts is to begin with not known. It is however imperative, before certain attitude change maneuvers can be carried out, that the initial attitude or orientation of the satellite can be precisely determined.
Thus there results the necessity, for instance during the transfer phase of a geosynchronous earth satellite prior to firing the apogee thruster, of bringing the satellite into an initial attitude favorable for this maneuver, to orient it for instance with its roll axis in the direction of the thruster impulse. A reference in three axes is required for attitude determination, which generally is given by the sun and the earth. The attitude determination and the reorientation of the satellite into the desired initial attitude for an apogee insertion requires a certain time period, and it can occur that, at the point in time of the attitude determination, a point on the path has been reached where sun, satellite and earth lie in one straight line and the three-axis reference is thus no longer available. The missing reference can be replaced by an integrating gyro, which on its part assumes its reference at an earlier geometrically more favorable instant, when a sufficiently accurately defined attitude of the satellite can be adjusted with the help of solar sensors and an earth sensor. Since however the gyro has an unknown drift to begin with, the attitude determination performed by said gyro directly prior to the reorientation of the satellite for the purpose of the apogee insertion can already comprise again such a high inaccuracy, that finally unacceptable directional errors arise during the apogee insertion. The gyro drift must be determined in order to avoid this, meaning the gyros must be calibrated or gauged. Then the gyro drift can be taken into account during the attitude determination.